We do know that not everybody at the funeral took part in the battle, some of them just came for Dumbledore.
An extraordinary assortment of people had already settled into half of the chairs: shabby and
smart, old and young. Most Harry did not recognise, but there were a few that he did, including
members of the Order of the Phoenix: Kingsley Shacklebolt, Mad-Eye Moody, Tonks, her hair
miraculously returned to vividest pink, Remus Lupin, with whom she seemed to be holding
hands, Mr. and Mrs. Weasley, Bill supported by Fleur and followed by Fred and George, who
were wearing jackets of black dragonskin. Then there was Madame Maxime, who took up twoand-a-half chairs on her own, Tom, the landlord of the Leaky Cauldron, Arabella Figg, Harry’s
Squib neighbour, the hairy bass player from the wizardmg group the Weird Sisters, Ernie Prang,
driver of the Knight Bus, Madam Malkin, of the robe shop in Diagon Alley, and some people
whom Harry merely knew by sight, such as the barman of the Hog’s Head and the witch who
pushed the trolley on the Hogwarts Express. The castle ghosts were there too, barely visible in
the bright sunlight, discernible only when they moved, shimmering insubstantially in the
Harry Potter and the Half Blood Prince, Chapter 30 (The White Tomb)
Seeing as "Most Harry didn't recognize" it's probable that they came from their homes for Dumbledore. Also, there are several characters that definitely weren't fit to fight i.e. Arabella Figg who was a Squib. As for Moody, he is never mentioned once during the Battle, so we can't be sure if he was there but it is possible he wasn't (and was otherwise employed). We also know that he wasn't positioned as a guard of Hogwarts at the beginning of the year.
“But what are you doing here, anyway?” Harry asked.
“I’m stationed in Hogsmeade now, to give the school extra protection,” said Tonks.
“Is it just you who’s stationed up here, or —?”
“No, Proudfoot, Savage, and Dawlish are here too.”
“Dawlish, that Auror Dumbledore attacked last year?”
Harry Potter and the Half Blood Prince, Chapter 8 (Snape Victorious)